GRAIN-SIZE EFFECTS ON THE TEXTURE EVOLUTION OF ALPHA-ZR

The texture evolution during the plastic deformation at room temperature of Zr-2.5Nb round bars was studied in specimens with two different alpha-Zr grain sizes. It was found that during axisymmetric compression the strain producing mechanisms active during deformation depended on the grain size. In fine grained specimens there are two main phenomena characterizing the evolution of texture: (i) a rapid rotation of the grains about their [c] axis to form a [11 (2) over bar 0] fiber at strains below -0.20 and, (ii) a slow and progressive reorientation of the [c] axes of the grains towards the compression axis to form a [0001] fiber texture tilted approx. 20 degrees. The latter process takes strains larger than -0.80. In coarse grained material, the texture evolution is characterized by a sudden rotation of the [c] axes to become aligned parallel to the compression axis at strains as low as -0.05. It is shown using a self-consistent viscoplastic model of texture evolution that the type of texture obtained depends on the mechanism controlling [c] axis deformation. In fine grained material prismatic slip, with basal and pyramidal [c + a] slip acting as complementary deformation modes, control the texture evolution process. In coarse grained material twinning is responsible for the final texture observed.